1. Field of the Invention
The present invention relates to a lamp using a semiconductor element like a light-emitting diode as a light source, and more particularly a structure for efficiently radiating the heat generated by a light source during lighting of a lamp.
2. Description of the Related Art
A light-emitting diode is well known as a light source for a lamp compatible with an incandescent lamp. The output of the light-emitting diode is lowered and the life is reduced, as the temperature is increased. Therefore, it is necessary to control the increase of the temperature of the light-emitting diode in the lamp using the light-emitting diode as the light source.
For example, Jpn. Pat. Appln. KOKAI Publication No. 2001-243809 discloses an LED lamp, which prevents overheat of a light-emitting diode by increasing the heat radiation of the light-emitting diode. The conventional LED lamp is provided with a spherical body, a metal substrate, and light-emitting diodes. The spherical body is composed of a metallic radiator having a base at one end and an opening at the other end, and a translucent cover. The metallic radiator has a shape spreading from one end to the other end like a bugle.
The metal substrate is fixed to the opening of the metallic radiator through a high heat conductivity member having electrical insulation. The light-emitting diode is supported by the metal substrate and covered by the translucent cover.
The heat generated by the light-emitting diode during lighting of the LED lamp is transmitted from the metal substrate to the metallic radiator through the high heat conductivity member. The heat transmitted to the metallic radiator is radiated to the atmosphere from the peripheral surface of the metallic radiator. This prevents overheat of the light-emitting diode, and increases the luminous efficiency of the LED lamp.
According to the LED lamp disclosed by the published Japanese patent applications, the metallic radiator to radiate the heat of the light-emitting diode and the metal substrate to mount the light-emitting diode are different components. In this structure, though the metal substrate and the metallic radiator are connected through the high heat conductivity member, it is unavoidable to generate a thermal resistance in a joint of the metal substrate and the metallic radiator. Thus, the conduction of heat between the metal substrate and the metallic radiator disturbed, and the heat of the light-emitting diode cannot be efficiently transmitted from the metal substrate to the metallic radiator. There is a point to be improved to control the temperature increase of the light-emitting diode.
Moreover, in the above-described LED lamp, a lighting circuit to light the light-emitting diode is an indispensable component. When the lighting circuit is incorporated in the LED lamp, it is requested that the size of the LED lamp is not increased by the lighting circuit. It is also known that when the temperature of the lighting circuit is increased, the reliability of the circuit operation is decreased and the life is reduced. Therefore, it is essential to prevent overheat of the lighting circuit when the lighting circuit is incorporated in the LED lamp.
The above-mentioned published Japanese patent applications do not describe about the lighting circuit. The LED lamps disclosed in these applications do not satisfy the demand for preventing the large size of the LED lamp and overheat of the lighting circuit.